Membranes have become invaluable tools in both the clinical and experimental biotechnological arts. Specifically, membranes are integral to immunodiagnostic assays and a variety of blotting assays. However, currently available membranes possess qualities which limit their utility within the context of the foregoing applications.
Immunodiagnostic assays are generally performed by applying a test liquid containing antigens to a porous membrane containing antibodies. As the test liquid laterally diffuses through the membrane, antibodies will bind antigens to which they are directed with a high degree of specificity. The binding of the antibodies to the antigens serves as a detection means (e.g., the visualization of the presence of antigens), and the specificity with which antibodies bind to antigens allows for the determination of whether or not the test liquid contains specific antigens. Therefore, in immunodiagnostic assays, the membrane desirably possesses optimal immunodiagnostic properties. In other words, it is desirable that the membrane allow for optimal lateral diffusion of the test liquid, allow for adequate visualization of the existence of antigens in the test liquid (i.e., the membrane is capable of a high signal-to-noise ratio), allow for adequate protein binding, is hydrophilic, is capable of being uniformly manufactured in order to yield consistent results, and is safe to use.
Similarly, in a blotting assay, a membrane is contacted with a fluid comprising biological molecules such that the biological molecules become fixed to the membrane. Biological molecules of interest are subsequently visualized. It is desirable that the membrane utilized within the context of blotting assays have optimal blotting properties. Specifically, it is desirable that the membrane allow for the adequate binding of biological molecules, allow for adequate visualization of the biological molecules of interest (i.e., the membrane is capable of a high signal-to-noise ratio), is hydrophilic, is capable of being uniformly manufactured in order to yield consistent results, and is safe to use. However, unlike those membranes used in immunodiagnostic assays, blotting membranes need not allow for the lateral diffusion of biological molecules. In fact, for most blotting applications (e.g., southern blots, northern blots, western blots, and in situ hybridization of bacterial colonies), lateral diffusion is undesirable.
The most common types of membranes available for use in immunodiagnostic and blotting assays include polyvinylidenefluoride, nylon, and cellulose-based membranes (e.g., nitrocellulose and cellulose acetate membranes). Each of the membranes, however, possesses qualities which limit its utility in the foregoing applications. Nitrocellulose is prepared by the nitration of naturally occurring cellulose. During nitration, a broad distribution of heterogenous oligomeric and polymeric nitrated products is produced as a consequence of the partial acid digestion of cellulose. Exacerbating the problem is the fact that the purity of the cellulose starting material depends on its source and pre-nitration treatment. As a result, uniformity in the manufacture of nitrocellulose membranes is difficult to achieve. For similar reasons, it is also difficult to achieve uniformity in the manufacture of other cellulosic membranes, such as cellulose acetate membranes. Furthermore, nitrocellulose membranes present numerous laboratory safety concerns by virtue of their flammability and explosiveness. Cellulose acetate and nitrocellulose membranes are also disadvantageous in that such membranes are very brittle, easily broken, and difficult to wet.
Nylon and polyvinylidenefluoride membranes also have disadvantages associated with their use within the context of the foregoing applications. Nylon membranes strongly bind biological molecules and, consequently, have low signal-to-noise ratios. Polyvinylidenefluoride and other synthetic polymeric membranes cannot be used in applications where surface activity, which facilitates the binding of biological molecules, is necessary or where high lateral flow rates are necessary.
In view of the foregoing problems, there exists a need for membranes which can be used more effectively in immunodiagnostic and blotting assays. The present invention provides such a membrane and methods for the preparation thereof. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.